Mounted in the ceiling and it has a leak, what may be the possible reasons it does this?

Evap coolers work by spraying water into the chamber, by pulling air through a foam belt or by running the air through a water bath. In any case, salts build up and have most likely plugged the drain pan tube. Clean the drain pan and either rod the drain tube out and/or pour vinegar down the pan drain pipe. I see your handle is Phoenix, good place for an evap cooler. Here in ATL, no can do.